Background of the Present Invention
The present invention refers to a drive unit for a centrifuge rotor of a centrifugal separator, wherein the drive unit includes a drive shaft, which is arranged to support said centrifuge rotor and rotatably journalled around an axis of rotation in at least one first bearing member, a casing, which forms an inner space for the drive shaft and said bearing member, and a drive motor, which is provided outside the casing and connected to the drive shaft by means of a transferring member extending through a passage in the casing.
In order to cool the bearings supporting the drive shaft in such a drive unit, it is known to re-circulate an air stream which, by means of accompanying oil droplets, forms an oil mist through the bearings and the inner space defined by the casing. Such drive units frequently include a drive belt for transferring the rotation of the drive motor to the drive shaft of the centrifuge rotor. In the cases that the drive motor is located outside the casing, the drive belt will either engage the drive shaft beneath the casing or extend through an opening in the casing. In order to prevent, in the latter case, oil from penetrating the environment and contacting the drive belt, the opening has to be sealed with respect to the drive belt. It has proved to be difficult to provide such an effective sealing. According to another solution, the drive motor may be provided inside the casing. However, this solution requires such an enclosure of the drive motor that oil is prevented from penetrating the drive motor and destroying the latter.
Another problem in this connection is the removal of the heat absorbed by the oil mist during its passage through the bearings, which support the drive shaft of the centrifuge rotor.
The object of the present invention is to remedy the problems mentioned above and provide a drive unit enabling a satisfactory sealing of the inner space of the casing with respect to the environment and enabling an effective cooling of the oil mist which is re-circulated in the inner space of the casing.
This object is obtained by the drive unit initially defined, which is characterised by a shielding member provided inside the casing in such a manner that the part of the transferring member which is located inside the casing is shielded from the inner space. Despite the fact that a part of the transferring member is located inside the casing, the whole transferring member, for instance in the form of a drive belt, will thus be separated from the inner space defined by the casing. No sealing of the transferring member is thereby required. Furthermore, such a shielding member enables an effective cooling of the different driving components by means of the surrounding air. The shielding member also creates a relatively large cooling surface extending in the inner space of the casing and thus contributes to the cooling of the oil mist, which is re-circulated in the inner space of the casing. Advantageously, the shielding member forms a channel, which extends through the casing and is shielded from the inner space of the casing.
According to an embodiment of the invention, the shielding member includes an upper opening and a lower opening, wherein the drive shaft extends through the shielding member through these openings. Sealing members may thereby be provided between the drive shaft and said openings. Thereby, the interior of the casing may, in an easy manner, be sealed from the environment and oil may be prevented from reaching the environment and the drive belt.
According to a further embodiment of the invention, the shielding member is connected to the casing by a connection extending around said passage. Furthermore, the shielding member may have an elongated shape with a longitudinal axis extending substantially radially with respect to the axis of rotation. The shielding member extends substantially diametrically through the casing with respect to the axis of rotation.
According to a further embodiment of the invention, the transferring member includes a drive belt which engages the drive shaft via a belt pulley provided on the drive shaft and thus located inside the shielding member. Such a drive belt will contribute to the creation of an air flow through the channel, thereby making the cooling more efficient. A wall member may thereby be substantially centrally provided in said channel in such a way that the channel is divided into two partial-channels and the drive belt may run inwardly in one of the partial-channels and outwardly in the other partial-channel. In such a manner, a first air flow from the environment will flow inwardly in one of the partial-channels and a second air flow will flow outwardly through the other partial-channel. The wall member extends in a substantially axial and radial plane with respect to the axis of rotation from an area in the proximity of the belt pulley to an area in the proximity of said passage. The drive shaft may be rotatably journalled in at least one bearing member located radially inside the drive belt.
According to a further embodiment of the invention, the transferring member includes a drive belt which engages the drive shaft via a belt pulley provided on the drive shaft and thus located inside the shielding member. Such a drive belt will contribute to the creation of an air flow through the channel and thereby making the cooling more efficient. Advantageously, a wall member may thereby be substantially centrally provided in said channel in such a way that the channel is divided into two part-channels and the drive belt may run inwardly in one of the part-channels and outwardly in the other part-channel. In such a manner, a first air flow from the environment will flow inwardly in one of the part-channels and a second air flow will flow upwardly through the other part-channel. Advantageously, the wall member extends in a substantially axial and radial plane with respect to the axis of rotation from an area in the proximity of the belt pulley to an area in the proximity of said passage. The drive shaft may be rotatably journalled in at least one bearing member located radially inside the drive belt.